It’s not just money left on the table, it’s a way to differentiate from the competition. When someone is trying to decide iPhones vs Android for their next purchase, being able to say “our OS doesn’t have ads” is big. I hear people complain about ads more than just about anything else.
I think users should have 0 tolerance for ads in the OS. It’s the broken window theory. Once they start, if the users don’t revolt, they will keep pushing them.
I find I don’t use the App Store much anymore. I used to browse it all the time, but it feels like one giant advertisement now.